In the LTE system, a UE sends Sounding Reference Signal (SRS) on time and frequency resources specified by a cell where it resides, for detecting the resident cell. An evolved Node B (eNodeB) in the cell estimates channel information from the UE to the eNodeB according to the SRS sent from the UE and the signal received by the eNodeB, as the basis for uplink frequency scheduling, MCS selection and resource allocation.
The power of the UE for transmitting the SRS is calculated based on an instruction of the eNodeB and path loss from the UE to its resident cell, specifically by use of equation (1), where PSRS(i) is the transmit power of SRS, i is a sub-frame number of the SRS, PCMAX is maximum transmit power of the UE, PSRS—OFFSET is a power parameter of the UE, MSRS is the bandwidth of the SRS transmission, PO—PUSCH(j) and f(i) are the same as corresponding power parameters of the PUSCH channel, PL is the path loss from the UE to its resident cell, α(j)·PL is the compensation amount of path loss.PSRS(i)=min{PCMAX,PSRS—OFFSET+10 log10(MSRS)+PO—PUSCH(j)+α(j)·PL+f(i)}  (1)
The eNodeB instructs the UE of SRS transmit power parameters (including PSRS—OFFSET, MSRS, PO—PUSCH(j), α(j) and f(i)) via a parameter configuration command; the UE calculates PL, and calculates the SRS transmit power according to equation (1) by use of PL, PCMAX and the received SRS transmit power parameters.
In the 3GPP LTE Advanced system, multi-point coordinated transmission technology is adopted to improve quality of service of cell edge users. The multi-point coordinated transmission technology uses joint scheduling or coordinated transmission of multiple cells geographically separated to improve quality of signals received by users and reduce inter-cell interference, thereby effectively improving spectral efficiency of edge users and system capacity. In the multi-point coordinated transmission technology, information of channels from a UE to more than one cell is an important factor affecting system performance. Then, there is a need for a UE supporting the multi-point coordinated transmission technology to perform channel detection for multiple cells, i.e., send SRS to the multiple cells. When the UE sends an SRS, equation (1) can still be used to determine the SRS transmit power. However, since path loss of the UE to each of the cells is different from each other because of the difference on distances from the multiple cells to the UE, it may appear that the SRS signal sent from the UE and received by an eNodeB far from the UE is weak if the SRS transmit power is still calculated in accordance with the path loss from the UE to its resident cell, leading to a poor accuracy of channel estimation.